Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands	3 Months Ended				6 Months Ended
	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Accounting Policies [Abstract]
Number of operating segments | segment					1
Number of reporting segments | segment					1
Net loss | $	$ 67,062	$ 32,860	$ 70,568	$ 67,904	$ 99,922	$ 138,472
Cash and cash equivalents used in operations | $					$ 110,576	$ 135,148